Oncostatin M, originally identified for its inhibitory effects on human tumor cell lines, was first isolated from phorbol 12-myristate 13-acetate (PMA)-induced human histiocytic lymphoma cells (Zarling et al., 1986, Proc. Natl. Acad. Sci. USA 83: 9739-9743) and from activated T lymphocytes (Brown et al., 1987, J. Immunol. 139: 2977-2983). The molecule is a heat and acid stable protein comprised of a single polypeptide chain M.sub.r =28,000. Like other naturally occurring growth regulators, Oncostatin M exhibits a variety of biological activities. Growth inhibition is observed with some, but not all, human tumor cell lines. In contrast, the growth of some normal fibroblasts, such as human foreskin fibroblasts or WI-38 cells, is stimulated by exposure to Oncostatin M (Zarling et al., 1986, Proc. Natl. Acad. Sci. USA 83: 9739-9743).
The gene for Oncostatin M has been cloned and sequenced, and an active form of recombinant Oncostatin M has recently been expressed in mammalian cells (copending U.S. Application Ser. No. 144,574 filed Jan. 15, 1988, which is incorporated herein by reference in its entirety). The mature form of Oncostatin M is a glycoprotein containing 228 amino acids, five of which are cysteine residues. The protein has an extremely hydrophilic carboxy terminal domain. Although Oncostatin M is not structurally related to other known cytokines, its mRNA contains an AU-rich region at its 3' untranslated end. This region in the Oncostatin M message is homologous to that of many cytokines, lymphokines and other growth-regulatory moelcules, suggesting a common mode of regulating gene expression. A cellular receptor for Oncostatin M has been found on a variety of mammalian cells. The major Oncostatin M receptor molecule is a specific protein of M.sub.r =150,000-160,000 (Linsley et al., 1989, J. Biol. Chem. 264: 6528 -6532).